1. Field of the Invention
The present invention relates to a variable oil pump, and more particularly, to a variable oil pump capable of, when oil is supplied to a power generating apparatus such as an engine, preventing the oil from being excessively supplied in a medium speed range and a high speed range, sufficiently supplying the oil in a low speed range and a medium/high speed range, and thereby preventing unnecessary supply of the oil with a simple structure.
2. Discussion of Related Art
In general, an engine requires a lubrication apparatus that can lubricate operating components such as a piston and a crankshaft. In particular, the lubrication apparatus requires an oil supply apparatus such as an oil pump that can supply a working fluid such as oil to places where a lubrication operation is needed.
In particular, a rotor-type oil supply apparatus is connected to a crankshaft to be used to adjust an ejected amount of a working fluid in proportion to an engine RPM. Accordingly, a flow rate of an ejected working fluid of a conventional oil supply apparatus is increased in proportion to the engine RPM.
However, since such an oil supply apparatus ejects the working fluid in proportion to the engine RPM regardless of a lubrication state of a portion at which lubrication is needed, fuel efficiency of the engine may be decreased. That is, at the beginning of the engine start of a vehicle, since the working fluid flows downward due to gravity, a larger amount of working fluid is needed to perform sufficient lubrication, and thus, the working fluid should be supplied in proportion to the engine RPM.
However, when a vehicle speed is at a medium speed and a high speed, since a sufficient amount of working fluid is already supplied, there is no need to supply the working fluid in proportion to the engine RPM. In addition, excessive supply of the working fluid at the medium speed and the high speed takes power consumption from the crankshaft, and thus, fuel efficiency of the engine may be decreased.
For this reason, various variable oil pumps configured to supply oil in proportion to a vehicle speed, etc., have been developed. Korean Patent Application No. 10-2005-0048151 (May 24, 2005) discloses a structure of such a variable relief valve. The structure of the variable relief valve, in which a valve chamber is provided at one side of an oil ejection port of an oil pump to adjust a pressure of oil pumped by the oil pump and an oil relief valve is elastically supported in the valve chamber by a spring 33 to drain the oil through a bypass hole formed in one side of the valve chamber according to an oil pressure passing through an oil line, is characterized in that a bimetal 40, a volume of which expands according to variation in temperature, is disposed between an upper surface of a cap 36 fixed to a lower portion of the valve chamber 31 to support a lower end of the spring 33 and a lower surface of a spring seat 37 movably provided at the lower end of the spring 33.
However, such a structure has the following problem. Since the valve is configured to be operated according to variation in temperature, it is difficult to rapidly vary the pressure of the oil, i.e., the oil pressure, according to variation in engine RPM.